Re: [EnergyPlus_Support] Ventilated and opened space between roof and cooled closed spaces (ExteriorNaturalVentedCavity?)

2014-07-08 9:54 GMT-05:00 'Edward G. Lyon' eglyon@xxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx>:

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I recently did something similar with an attic space for an unconditioned building.Â I made the attic a zone and used airflownetwork to ventilate it through existing openings.Â I could then look at the effectiveness of insulation placement and amounts.Â Once I had an effective attic design, I scheduled the attic ventilation based on the last airflownetwork analysis and then worked on my occupied zones.

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Ned Lyon, P.E. (MA, WV)
Staff Consultant

SIMPSON GUMPERTZ & HEGER
781.907.9000Â main
781.907.9350 directÂ
617.285.2162 mobileÂ
781.907.9009Â fax
www.sgh.com

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From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Tuesday, July 08, 2014 10:06 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Ventilated and opened space between roof and cooled closed spaces (ExteriorNaturalVentedCavity?) [2 Attachments]

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Hi all,

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Iâ??m trying to model the effect of a separated roof in a hot humid climate.

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I join 2 pictures, hoping it will help you to understand the idea. In a simple way, I have various closed (occupied and cooled) volumes, with a large separated roof that protects these volumes from direct solar radiation.

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Iâ??d like to see the radiative and convective effect of such a roof (for example depending on its construction) on the roof of the volumes, in order to decrease the cooling loads.

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The matter is that Iâ??m wondering how to model that. Iâ??m thinking about using the GapConvectionRadiation and SurfaceProperty:ExteriorNaturalVentedCavity, but Iâ??m not sure it will match perfectly, because the cavity is mainly opened to exterior conditions, such as wind (although itâ??s not very high: 2 a 3 m/s averagely).

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I see 3 options:

- Assuming the roof as a solar protection. But this way, i canâ??t give it thermal properties (as Iâ??d do with an â??attachedâ?? roof), or maybe the ShadingProperty:Reflectance object (i just want to get a correct radiation from the "interior" roof's surface)? In this case, may I give the â??Area Fractions of Openingsâ?? the opened surface?Â Would that be OK according to you?

- Should I assume the cavity as a thermal zone, with mainly AirWall as vertical surfaces?? In this case, I think I woulld get to a complex place, having to model natural ventilation in a tough way, donâ??t you think? Not even sure it would workâ?¦

- maybe the simplest way would be to give to my roofâ??s volume (not the big one that protects from solar radiation, but the one of the closed volumes) an Outside Boundary Condition and Outside Boundary Condition Object with a GapConvectionRadiation?

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I would be really grateful if some of you could tell me which of these options looks correct, or if you could give me other suggestions according to that kind of simulations!

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Thanks for your attention. I hope Iâ??ve been clear.

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Regards,

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Mathieu